With the requirements of high performance and high efficiency, the operating frequency of electronic components is getting larger and larger. As a result, the quantity of heat so produced is increasing day after day. However, the advancement of science and technology makes electronic products to follow the trend of a light, thin, short and compact design. The reduced size also increases the quantity of electronic components per unit volume, and thus results in a trend of giving out heat in a high thermal flux density. Since the operating temperature of an electronic component is closely related to the reliability and the life of the electronic component, therefore the way of effectively enhancing the heat dissipating capability becomes a key issue, particularly in the field of electronic peripherals of notebook computers that is restricted by volume and size.
Since the design and performance of different electronic components are different, the heat flux is unevenly distributed at different positions of an electronic product and the so-called hot spots will be produced on the surface due to different local temperatures. To solve the problem, manufacturers develop an even heat dissipating device with a capillary structure to overcome the foregoing shortcomings. A heat pipe is an example of such applications, and the principle of its actions resides on injecting a volatile working fluid such as water or alcohol into a sealed container or forming a low pressure in such sealed container and having a capillary structure therein. The working fluid is converted into gas phase after absorbing heat from the heated side, and the gas-phase working fluid is condensed into liquid phase under a lower temperature. The heat is discharged by the high latent heat effect of the gas/liquid phase conversion process, and then flows back to the heated side through the capillary structure, and thus constituting a circular heat dissipation operation.
Please refer to FIG. 1 for the cross-sectional view of a prior art liquid/gas phase heat dissipating device, which is a sealed metal cavity 10 having a capillary structure layer 11, a heated end (vaporizing end) 12, and a cooling end (condensing end) 13. The sealed metal cavity 10 contains a working fluid, and the working fluid is a liquid selected from pure water, ammonia solution, methyl alcohol, ethyl alcohol and acetone which has a high mobility and absorbs large quantity of heat when evaporated.
The principle of heat dissipation is to use the working fluid to transfer the heat produced by the electronic components as indicated by the arrows in FIG. 1 from the heated end 12 to the cooling end 13, and the capillary structure layer 11 of the sealed metal cavity 10 is used to proceed with the cycle of evaporation and condensation.
Although the capillary structure of the present even heat dissipation device provides the mobility for the liquid, yet the tension of the capillary is related to the contact surface and the material performance. As to water, a better hydrophilic surface has a smaller contact angle and a better mobility, and thus provides better performance for the capillary tension and the backflow of the liquid.
As to the general liquid/gas phase heat dissipating device and water is taken, as an example of the working fluid, since the material adopted by the device needs to have a better thermal conductive coefficient for a better heat dissipation effect. At present, the metal including copper or aluminum having a better thermal conductive is used for the basic material, but copper will react with the oxygen in the air to produce copper oxide and aluminum will react with oxygen to produce aluminum oxide. As a result, the contact angle between the inner wall of the capillary structure and water is too large, and thus the mobility of water is lowered and the heat dissipation effect is reduced. If other methods are used to enhance the capillary tension such as changing the size of the capillary structure or eliminating the impurities on the surface, the cost for the manufacturing technology and expenditure required for such change will be increased. Even after the size of the capillary structure is accomplished, the contact angle between the surface of the capillary structure becomes smaller, but the property of the basic material of the surface of the capillary structure is still not improved, and thus the mobility of the working fluid has not been improved thoroughly.
If copper is used as the material for manufacturing the even heat dissipating device containing a working fluid, the manufacturing procedure includes rinsing the copper pipe first to reduce the contamination of impurities and assuring its performance. However, the general rinsing procedure takes lots of manpower, and if related chemical rinsing agents such as a pickling or an organic solvent are used for the rinse, such arrangement not only increases the cost, but also contaminates the environment. Most importantly, the oxidation capability after the rinse is not good. Once the copper pipe is oxidized, then the mobility of the working fluid will be further lowered.
The prior-art heat dissipation devices having a capillary structure as disclosed in the U.S. Pat. No. 6,158,502 published on Dec. 12, 2000 and the U.S. Pat. No. 6,167,948 published on Jan. 2, 2001 come with a diversification design of the capillary structure. Besides the size and arrangement of the capillary structure, there is no significant improvement on the property of the surface of the capillary structure. Other heat dissipating devices having a capillary structure have been disclosed in many R.O.C. patent applications such as the R.O.C. patent application Publication No. 563,016 published on Nov. 21, 2003 which disclosed a method of manufacturing a heat pipe, the R.O.C. patent application Publication No. 528,151 published on Apr. 11, 2003 which disclosed a heat dissipating device adopting a two-layer capillary structure instead of a single-layer capillary structure, and the R.O.C. patent application Publication No. 501,722 published on Sep. 1, 2002 which disclosed a heat dissipating device using a different form of copper grids to produce the capillary structure. However, the foregoing prior arts did not teach how to improve the surface contact of the working fluid and the capillary structure.